Coated backing sheet and stencil-sheet assembly embodying same



Nov. 21, 1961 P. E. FRASHER ET AL 3,009,416

COATED BACKING SHEET AND STENCIL-SHEET ASSEMBLY EMBODYING SAME Filed April 24. 195'! {/2 /6 N\ I 5 K\\ m W I /A INVENTOR.

PAUL E. FRASHER BY JOHN J- REKIH United States fiice 3 009,416 COATED BACKING SI IEET AND STENCE-SHEET ASSEMBLY EMBODYING SAME Paul E. Frasher and John J. Reich, Chicago, Ill., assignors to A. B. Dick Company, Niles, 111., a corporation of Illinois Filed Apr. 24, 1957, Ser. No. 654,766 9 Claims. (Cl. 101--128.2)

This invention relates to a stencil sheet assembly, and it relates more particularly to the assembly of a stencil sheet with a backing sheet as supplied for use in the preparation of a stencil for ofiice copy work.

In general, a stencil sheet is supported on a backing sheet to provide an assembly which can be handled more easily for imaging as by a typewriter or the like. The backing sheet is separable from the imaged stencil sheet and, for this purpose, perforations are usually provided along the edge where the two are joined.

In the present practice, use is also made of a cushion sheet which is interleafed between the backing sheet and the back side of the stencil sheet. The cushion sheet is usually provided with a colored coating on the surface adjacent the stencil sheet and it is the function of the cushion sheet to increase the visibility or readability of the image that is formed during stencilization and to give a broader and more readable copy. Usually the cushion sheets are supplied separate and apart from the stencil and the backing sheet assembly because of the many difficulties that arise from full and continuous contact between the coated cushion and the coated stencil. Very often one cushion sheet may be employed with three or four stencils.

There are a number of objections to the practice as presently employed. Considerable inconvenience arises from the necessity carefully to insert the cushion sheets between the stencil and the backing sheet and to remove the cushion sheet from between the imaged stencil and the backing sheet to enable reuse of the cushion in subsequent stenciling operations. Considerable time is lost in effecting such assembly and disassembly, while additional space is required for storage of cushion sheets.

Thus, it is an object of this invention to overcome these inconveniences and to produce a stencil sheet assembly which does away with the need for a cushion sheet in the preparation of the stencil.

More specifically, it is an object of this invention to produce a stencil sheet assembly which can be easily and efiiciently manufactured of readily available and inexpensive materials; which can be employed as supplied without the need for use of additional elements in combination therewith during the stencilizing operation; which provides for good readability during preparation of the image without the use of a cushion sheet; which does not interfere with the stencil sheet or the coating thereon, and which operates to give broad and readable copy of the character heretofore available from the use of cushion sheets in combination with the stencil sheet assembly.

These and other objects and advantages of this invention will hereinafter appear and, for purposes of illustration, but not of limitation, an embodiment of the invention is shown in the accompanying drawing in which FIGURE 1 is a perspective elevational view of a stencil sheet assembly embodying the features of this invention, and

FIGURE 2 is a fragmentary sectional view taken along the line 2-2 of FIGURE 1.

In accordance with the practice of this invention, the need of a cushion sheet in a stencil sheet assembly is avoided by use of a backing sheet 10 having a coating 12 on the side underlying the stencil 14, which coating provides the functions heretofore derived from the use of a cushion sheet without the disadvantages which have been inherent therein.

Use has previously been made of coated backing sheets in stencil sheet assemblies, but such coated backing sheets as have heretofore been produced have been impractical because of their deleterious effect of the coating and components thereof on the stencil. For example, it was found that the utility of the stencil decreased sharply when aged in contact with coated backings of the type heretofore produced, as evidenced by the falling out or displacement of loop letters during use of the stencil in the production of copy. This resulted in the production of copy having various distortions and breaks, to the end that copy of poor quality was secured. In addition, adhesion between the stencil coating and the coating on the backing sheet often resulted in displacement of the stencil coating to the backing sheet during separation of the sheets, with the result that undesirable openings were formed in the stencil. In the alternative, coating often transferred from the backing sheet to the stencil with resultant interference in the subsequent use of the stencil for the production of copy.

The improvement forming the subject matter of this invention resides in the fabrication of a stencil sheet assembly having a backing sheet formed with a coating characterized by the ability to obviate many of the difficulties heretofore encountered in the use of a coated backing sheet.

In the drawing, 14 represents a coated stencil of conventional construction secured along its upper edge 16 to the upper edge of the backing sheet 10. The backing sheet is provided with perforations 18 across its upper edge immediately beneath the attachment to enable the backing sheet to be ripped from the stencil following the stencilization and prior to mounting the stencil'sheet in the duplicating machine for use in producing copy. In the typing area, the backing sheet is provided with a coating 12 on the upper surface thereof in positionentirely to underlie the stencil sheet '14.

In its broadest concepts, the coating is formulated of a base formed of a polyolefine, such as polypropylene, polybutene and the like, and preferably polyethylene, which shall be employed hereinafter as representative of this group of materials. The polyolefine or polyethylene resin should be of low molecular weight, such as within the range of 1,000 to 10,000 molecular weight, and pref erably having a molecular-weight average within the range of 2,000 to 5,000. While the polyolefine or polyethylene resin may be used alone as the coating applied to the backing sheet, it is preferred to embody a filler into the coating composition in an amount which may range from 0 to 20% by weight of the coating composition, and preferably in amount ranging from 5 to 20%': Where a tinctorial agent is desired to impart by weight. a color for contrast with the stencil sheet, thereby to impart visibility and readability to the formed stencil, coloring agents such as lakes, toners or pigments may be incorporated in an amount ranging from 0 to 20% by pigment, greater amounts may be employed, but an' amount greater than 20%-by weight of the coating composition is seldom required.

As the filler, use can be made of such materials as calcium carbonate, calcium sulfate, diatomaceous earth, silica, and the like filler materials of inorganic or siliceous nature. When the pigment is capable of functioning also as a filler in the coating composition, as when use is made of carbon black, white lead, titanium dioxide, and the like, the amount of additional filler may range from 1 to 10% by weight of the coating composition. When the coloring material is incapable of concurrent function as a filler, then it is desirable to employ greater amounts of filler, such as in the range of to 20% by weight.

The following will be the practice of this invention.

EXAMPLE I Coating composition Percent by weight Low molecular weight polyethylene (1700 M.W. aver- The polyethylene is heated to a molten state and the other materials are blended in. The coating composition is applied as a hot melt onto the paper making up the backing sheet. Application is made in coating weights of about 4 to 18 pounds per 3,000 square feet of surface area. The coating sets upon cooling, and the coated paper is sheeted to the form of backing sheets which are perforated near their edges and then collated for combination with the stencil sheet. The two are secured together by adhesives near their upper edges beyond the perforated portion of the backing sheet.

For certain applications, it is desirable to have greater flexibility and softness in the coating of the backing sheet, such, for example, as to enhance the cushioning effect on the stencil and for the development of other desirable characteristics. These properties can be achieved in a coating composition of the type described by formulation of the polyethylene coating composition to include a softener and flexibilizer, as represented by mineral oil, polybutene, chlorinated diphenyls, and the like plasticizers and softener materials. While these materials ordinarily are incompatible with most polyethylene resins, it has been found that in the molecular-weight range of the polyethylene, and in the amount of the other ingredients employed in combination therewith, sufiicient compatibility is secured to enable the formulation of a clear and stablecomposition for application as a hot melt in the described coating weights to the backing sheet. When such softening and flexibilizing agents are employed, it has been found best to make use of an amount within the range of 5 to 40% by weight of the coating composition, and preferably an amount within the range of to by weight of the coating composition.

- By way of still further modification, use can be made of a parafiin wax in combination with the polyethylene (with or without filler and pigment) to produce a tough and flexible coating having good resiliency and good adhesion to the backing sheet without the development of sticking to the coating of the stencil. Representative of the parafiin waxes which may be employed are parafin, cardis wax, and the like. There may be also included a small amount of a fatty acid, such as stearic acid and the like. When such paraffin-wax component is employed, the concentration thereof in the coating composition may range from 20 to 70% by weight, and preferably in an amount ranging from 40 to 60% by weight.

The following coating compositions are representative of the further modifications which may be employed for use in production of coated backing sheets.

EXAMPLE II Percent Polyethylene (Allied Chemical #6) 64 Diatomaceous earth 12 Titanium dioxide 4 Mineral oil 20 EXAMPLE III Polyethylene (Allied Chemical #615) 30 Paraflin wax-l35137 l /I.P 46 Oardis wax 3 Stearic acid 1 Carbon black 20 EXAMPLE IV Polyethylene 65 Finely divided silica l4 Toner or lake 1 Polybutene 20 The above compositions are applied as a hot melt at a temperature of 250 to 350 F. in coating weights of from 4 to 18 pounds for 3,000 square feet of surface area.

The coating formed on the backing sheet can remain in contact with the coated stencil without extracting materials from the stencil, or without other undesirable eflfects thereon thereby to enable the assembly to be aged together over extended periods of time without deterioration of the coated stencil and without undesirable effect on the stencilization thereof, or in the use thereof to produce copy or in the copy that is produced therefrom.

The coated backing sheet operates in combination with the coated stencil to provide the function of a cushion sheet without the inconvenience inherent in the use of such sheet for stencilization. The coated backing sheet, while more expensive than backing sheets of the type heretofore produced, represents a more economical assembly when compared to the combination previously employed of a backing sheet and stencil sheet with a cushion sheet interleaved therebetween, and the coated backing sheet provides for an assembly which is more economical and more efficient in use.

It Will be understood that invention resides not only in the coated backing sheet, but also in the combination thereof with the stencil sheet to form a new and improved stencil sheet assembly. It will further be understood that changes may be made in the details of formulation and application without departing from the spirit of the invention, especially as defined in the following claims.

We claim:

1. A stencil sheet assembly having as its only components a stencil sheet removably attached to a coated backing sheet underlying the stencil sheet, with the coating on the backing sheet underlying the imageable portion of the stencil, consisting essentially of at least 60 percent by weight of a low molecular weight polyolefin selected from the group consisting of polyethylene, polypropylene, and polybutene, said polyolefin having an average molecular weight of not greater than 10,000, from 0 to 20 percent by weight of a tinctorial agent, and from 0 to 20 percent by weight of an inorganic filler.

2. A stencil sheet assembly having as its only components a stencil sheet removably attached to a coated backing sheet underlying the stencil sheet, with the coating on the backing sheet underlying the imageable portion of the stencil, consisting essentially of at least 60 percent by weight of a low molecular weight polyolefin selected from the group consisting of polyethylene, polypropylene, and polybutene, said polyolefin having an average molecular weight of not greater than 10,000, from 0 to 20 percent by weight of a tinctorial agent, from 0 to 20 percent by weight of an inorganic filler, and from 0 to 40 percent by weight of a fiexibilizing agent.

3. A stencil sheet assembly having as its only components a stencil sheet removably attached to a coated backing sheet underlying the stencil sheet, with the coating on the backing sheet underlying the imageable portion of the stencil consisting essentially of at least 60% by weight of a low molecular weight polyethylene having an average molecular weight of not greater than 10,000, from to 20% by weight of a tinctorial agent and from 0 to 20% by weight of an inorganic filler.

4. A stencil sheet assembly having as its only components a stencil sheet removably attached to a coated backing sheet underlying the stencil sheet, with the coating on the backing sheet underlying the imageable portion of the stencil consisting essentially of at least 60% by weight of a low molecular weight polyethylene having an average molecular weight of not greater than 10,000, from 0 to 20% by weight of a tinctorial agent, from 0 to 20% by weight of an inorganic filler, and from 0 to 40% by weight of a flexibilizing agent.

5. A stencil sheet assembly having as its only components a stencil sheet removably attached to a coated backing sheet underlying the stencil sheet, with the coating on the backing sheet underlying the imageable portion of the stencil consisting essentially of at least 60% by weight of a low molecular weight polyethylene having an average molecular weight of not greater than 10,000, from 0 to 20% by weight of a tinctorial agent, from 0 to 20% by weight of an inorganic filler, and from 0 to 40% by weight of a flexibilizing agent from the group consisting of mineral oil, polybutene and chlorinated diphenyl.

6. A stencil sheet assembly having as its only components a stencil sheet removably attached to a coated backing sheet underlying the stencil sheet, with the coating on the backing underlying the imageable portion of the stencil consisting essentially of from 30 to 80% by weight of a low molecular weight polyethylene having an average molecular weight not greater than 10,000 and from 20 to by weight of a paraffin wax.

7. A stencil sheet assembly having as its only components a stencil sheet removably attached to a coated backing sheet underlying the stencil sheet, with the coating on the backing underlying the irnageable portion of the stencil consisting essentially of from 30 to by weight of a low molecular weight polyethylene having an average molecular weight of from 2,000 to 5,000 and from 20 to 70% by weight of a parafiin Wax.

8. A stencil sheet assembly as claimed in claim 6 wherein the coating composition also contains a small amount of a saturated fatty acid.

9. A stencil sheet assembly having as its only components a stencil sheet removably attached to a coated backing sheet underlying the stencil sheet, with the coating on the backing sheet underlying the imageable portion of stencil sheet consisting of at least 30% by Weight of a low molecular weight polyethylene having an average molecular weight of not greater than 10,000, from 5 to 40% by weight of a paratfin wax, from 1 to 20% by weight of a tinctorial agent and from 1 to 20% by weight of a filler.

References Cited in the file of this patent UNITED STATES PATENTS 1,741,029 Kurth Dec. 24, 1929 2,203,280 Heath June 4, 1940 2,732,795 Brandt et a1. Jan. 31, 1956 

1. A STENCIL SHEET ASSEMBLY HAVING AS ITS ONLY COMPONENTS A STENCIL SHEET REMOVABLY ATTACHED TO A COATED BACKIN SHEET UNDERLYING THE STENCIL SHEET, WITH THE COATING ON THE BACKING SHEET UNDERLYING THE IMAGEABLE PORTION OF THE STENCIL, CONSISTING ESSENTIALLY OF AT LEAST 60 PERCENT BY WEIGHT OF A LOW MOLECULAR WEIGHT POLYOLEFIN SELECTED FROM THE GROUP CONSISTING OF POLYETHYLENE, POLYPROPYLENE, AND POLYBUTENE, SAID POLYOLEFIN HAVING AN AVERAGE MOLECULAR WEIGHT OF NOT GREATER THAN 10,000, FROM 0 TO 20 PERCENT BY WEIGHT OF A TINCTORIAL AGENT, AND FROM 0 TO 20 PERCENT BY WEIGHT OF AN INORGANIC FILLER. 